What are the most popular wrong scientific explanations for why humans walk upright?
As new evidence is discovered, we always can change our minds, right? But one wrong idea that’s still with us—the basis of 2001: A Space Odyssey—is we were a violent species from the get-go and evolved bipedalism to free our hands for weaponry....
That famous image is called “March of Progress.” Tell us about it.
“March of Progress” was an illustration done by a Russian artist, Rudolph Zallinger, in a 1965 Time-Life book called Early Man. It’s this beautiful foldout that shows ancient apes down on all fours, and it has them slowly rising up to modern humans. At the time, with the fossils we had, you could create a narrative like that. But in the last half century we’ve made so many amazing discoveries that show the human family tree is much more diverse. The pace of evolutionary change is quite different and it turns out that upright walking is the earliest of these evolutionary changes. The earliest bipeds on the ground were evolving from things that were upright to begin with in trees. Really all that happened was an ecological change....
It’s a misnomer, isn’t it, to think only one hominin existed at a time?
It is. One of the things we’re learning from new fossil discoveries is there appears to be these different species of early human, or hominin, coexisting on the landscape with different anatomies or adaptations in their feet and legs....
How do paleoanthropologists know early hominins were cooperative?
One of the best pieces of evidence we have is a fossil of an individual who’s broken a leg bone, a femur. This is long before hospitals, doctors, casts, anything like that. The beauty of the fossil is you can see a healed fracture. Imagine 2 million years ago, you break your leg. There’s no way you should survive. But a hominin did. The key word is healed. He survived that trauma. I don’t think he could have done that alone.
Did bipedalism lead to cooperation?
I think so....
Maybe it’s better to say cooperation is a byproduct of being a vulnerable biped.
That’s exactly right....
Energy is a zero-sum game, right? There’s only so much energy available and the body allocates it to the most demanding organs?
That’s right. One of the hypotheses about brain growth is derived from what’s called the “expensive tissue hypothesis.” Energy is allocated to the brain, but where are you getting that energy from? The argument is the digestive system. Essentially the intestines reduce in volume, and by reducing that expensive tissue, you’re able to allocate more energy to a larger brain....
Is there a larger message about evolutionary biology in our anatomical problems?
Yes, and it comes back to what we were talking about before. Humans buffer themselves with culture. Is natural selection still operating on humans? Absolutely. It has for the last 6 million years. Our foot anatomy may be suboptimal and lead to problems. But we solve our problems culturally and socially....